This disclosure describes a processing approach for the rapid and efficient in-situ polymerization of specially prepared precursor mixtures to achieve near-net-shape production of objects/articles with exact dimensions. The process relies on the use of polymerizable compositions comprised of a mixture of a dead polymer, a reactive plasticizer and an initiator, which compositions are semi-solid-like prior to curing and induce low shrinkage upon curing as a result of their partially polymerized nature prior to processing. The partially polymerized nature of the precursor mixtures also allows extremely impact-resistant objects/articles to be fabricated. Other desirable engineering property attributes can similarly be achieved via the judicious blending of starting ingredients in formulating the polymerizable (curable) mixtures.

This invention is related to the fields of polymerization and molding. More particularly, it is related to a process for the rapid in-situ near-net-shape polymerization of semi-solid-like materials to provide objects that are dimensionally stable and precise, with very little shrinkage upon curing. The invention is further related to semi-solid-like materials useful with the process.
Dimensionally precise objects/articles find numerous applications in electronics, optics, automotive, aerospace, and other high-technology industries. Examples include optically transparent objects/articles such as various precision lenses (spherical and aspherical), ophthalmic lenses (single vision, bifocal, trifocal, and progressive), contact lenses, optical data storage disk substrates, and projection optics/lens arrays. Non-transparent but dimensionally exact parts abound, such as couplers, housings, gears, and various packaging assemblies. The most straightforward fabrication method for dimensionally precise parts is the machining, grinding, and polishing of sheet stock and, in fact, this approach is still used today for some types of ophthalmic lenses. Unfortunately, this approach is limited to simple geometries and is costly due to the relatively large amounts of skilled labor required to produce a single part. More commonly, the plastics industry relies on well-known processes such as injection molding, compression molding, transfer molding, reactive injection molding (RIM), and casting for the fabrication of geometrically complex parts.
Injection molding, compression molding and transfer molding require the use of thermoplastic polymers. Material choices are limited to uncrosslinked polymers that can be melted by heat and injected at high pressures. Example polymers include polymethylmethacrylate, polystyrene, ABS (acrylonitrile-butadiene-styrene) and polycarbonate. These molding processes entail high temperature and pressure; therefore, expensive molding equipment and molds are necessary. Large parts with thick cross-sections are difficult to mold, since the heat transfer rate is slow. Long cycle times make the processes uneconomical. Additionally, finite coefficients of thermal expansion can lead to part warpage upon cooling. Thus, these processes are seldom practical for large-scale manufacturing of truly dimensionally demanding parts.
Reaction injection molding requires the use of at least two highly reactive components (A+B). Urethane is one such example, where the reactive components are monomeric isocyanates and alcohols. The components are quickly and thoroughly mixed just before injection into the mold cavity. The material is then allowed to quickly set in the cavity (cured). This methodology relies on materials that are highly reactive and generally toxic. Mechanical means for thorough mixing is part of the integral process, making the production equipment costly. The fabricated parts are also not quite dimensionally exact due to shrinkage effects associated with the polymerization process. Material selection is limited by the required reaction chemistry, as well. Thus, reactive injection molding (RIM) is limited by the need for highly reactive functional groups, the intensity of mixing prior to mold fill, and complex and expensive machinery to carry out the process.
Fabrication of precision parts has been attempted by processes generally known as casting. Casting is typically a less expensive alternative to the above processes. It is also a more flexible process, in that a great number of precursor mixtures (e.g., monomers, crosslinkers, oligomers, etc.) can be formulated to achieve different final parts and performance properties. The final parts can be thermosets, formed by a polymer network that is crosslinked to prevent melt flow. Since the precursor solution has a relatively low viscosity to facilitate mold fill, the process is a low-pressure operation, reducing the necessary equipment cost. The casting process, unfortunately, is often compromised by the high shrinkage rate of the formulated precursor mixtures, yielding inexact parts with warped shapes. The high shrinkage rate is a natural consequence of using precursors that have low to moderate viscosities. If we take an ophthalmic lens as an example, the mold defining the lens-shaped cavity generally consists of a front and a back half, and an intervening gasket. The front mold half is concave, whereas the back mold half is convex. Detailed design features distinguish the utility of the resulting lens. Hence, simple vision, bifocal, trifocal, progressive, spherical, aspherical, and toroidal lenses can all be made, in principle, but if and only if the in-situ curing process can be performed with near net-shape fidelity. This is obviously a difficult task, at best, if the material used for casting exhibits a high degree of shrinkage. Casting thus requires a mold-filling step, an activation step to trigger and sustain polymerization, and a mold-opening/ensuing cleaning step to finish the part and to recycle/re-shelf the mold halves. To date, all known casting processes begin with a polymerizable fluid that can be easily fed into the mold cavity, i.e., at moderate pressures. Care is necessary to minimize bubble creation. A carefully designed gasket is required, applied to seal off the cavity formed by the mold halves. Then a controlled curing step is imposed to convert the liquid feed into a finished, solid object.
Most curable formulations contain carbon-carbon double bonds. Such unsaturated sites are exemplified by functional groups like acrylates, methacrylates, vinyl ethers, and vinyls. Free radical or ionic polymerization mechanisms can be induced by the appropriate initiators, triggered by either UV or heat, i.e., photo- or thermally-induced polymerization. Since the reaction mixtures must fill the cavities in as short a time as possible to allow reasonable process economies, small-molecule or oligomeric mixtures are usually employed to keep viscosities low. These systems have a significant degree of shrinkage upon cure, as high as 15% for some oligomeric mixtures, and even greater than 20% for some small molecule formulations.
Additionally, the polymerization of unsaturated species is unfortunately an exothermic reaction. When such a reactive system is cured a great deal of heat is generated. The result is a spurious temperature excursion of the cast part during cure which often leads to thermal degradation of the material, discoloration, and part warpage upon cool down and removal from the mold. This problem may be reduced by improving heat transfer. Unfortunately, heat transfer can be improved only so much, due in part to the poor thermal conductivity of most polymeric systems. Overheating during cure can also be reduced by lowering the concentration of initiator species in the starting formulation, except that decreasing the initiator concentration prolongs the curing process and can lead to incomplete curing reactions and only partially polymerized final objects.
The heat generation and shrinkage accompanying polymerization must be accommodated by specially engineered curing processes, such as zone-curing techniques, in order to produce exact parts that replicate the contours of the cavity, and to slow the curing reaction so as to reduce spurious temperature rises. The need to use a gasket to prevent leakage (material escape) and minimize introduction of air bubbles dictates limited flexibility of mechanical design. It is also difficult to have the front and back mold halves positioned in such a way so as to intentionally create a non-aligned axial offset (known as de-centration). In addition, it is difficult to have the two axes rotated to create an intentional tilt (thus introducing a prismatic effect to the ensuing lens).
Finally, since most if not all of the reactive mixture exists initially in an unpolymerized state, the process must accomplish the curing of all such as-yet unreacted material precursors so that no small-molecule, volatile species remain in the finished part. This has the effect of protracting the process duration, especially if the initiator composition is kept low so as to minimize rate of heat generation. In free radical polymerization, this problem is further exacerbated by the reaction inhibition which occurs as a result of the presence of oxygen (either dissolved in the polymerizing liquid, or present in the vapor space surrounding the mold). Nitrogen purging of both the polymerizing liquid and of the mold cavity must be employed to keep oxygen levels low so that polymerization may occur in a timely fashion. Often nitrogen purging is not able to remove all oxygen, and parts remain only partially cured, especially near the part surfaces, leading to sticky or tacky skins. Manufacturers have gone to great lengths in order to prevent oxygen from slowing the cure reaction in the near-surface region of cast parts, often employing initiators that react with oxygen diradicals, high levels of initiators (which increases the likelihood of high-temperature excursions and yellowing), or oxygen impermeable films at the surfaces of the cured parts. Insertion of such films entails opening the mold after partially curing the object, which further has the effect of complicating the process and protracting the process duration.
The present invention discloses a revolutionary approach that overcomes the above described intrinsic drawbacks of commercially established processes. It is unique in that it has the promise of becoming an extremely economical process suitable for mass manufacture. It also gives parts that are dimensionally exact. Another aspect of this disclosure is the formulation of a new class of polymerizable materials that exhibit a semi-solid-like behavior during molding, very low inherent shrinkage upon curing, and highly optimized engineering properties of the final object.
More particularly, this invention is directed to a process for the rapid in-situ near-net-shape polymerization of semi-solid-like materials to provide a cured resin material characterized by one or more macromolecular networks resulting in articles of manufacture that are dimensionally stable and precise, with very little shrinkage upon cure. The process includes the steps of mixing together a dead polymer, a reactive plasticizer and an initiator to give a semi-solid polymerizable composition; shaping the semi-solid composition into a desired geometry; and exposing the polymerizable composition to a source of polymerizing energy, to give a final product with dimensional stability and high-fidelity replication of an internal mold cavity. The article so produced can optionally be transparent and/or have resistance to impact (resilient). The resulting macromolecular network is characterized as having either i) a semi-interpenetrating crosslinked polymer network of reactive plasticizer wrapped around and within an entangled dead polymer (semi-IPN); or ii) an interpenetrating crosslinked polymer network of reactive plasticizer within an entangled dead polymer, the reactive plasticizer polymer network being further crosslinked to the dead polymer; or iii) interpenetrating reactive plasticizer polymer chains, which may be linear, branched, etc., within an entangled dead polymer. In the extreme, very little to none of the dead polymer is used and only reactive oligomers or reactive macromers are used, as long as the material can be handled as a semi-solid. Upon polymerization, this arrangement leads to an entangled polymer (linear, branched, etc.) or to a single, uniform, crosslinked polymer network.
The reactive plasticizer may react with the dead polymer chains if the polymer has crosslinkable groups. In the presence of multifunctional monomers, two polymer networks are formed that are crosslinked together. Grafting reactions by chain transfer to the dead polymers may also occur in addition to the reactive plasticizer network formation among the dead polymers. Such systems are desirable because crosslinking of the dead polymer to the network formed by the reactive plasticizer can prevent phase separation between the two polymers. If only mono-functional reactive plasticizers are used, linear polymeric chains may be formed among the dead polymer chains. This arrangement will generally not be preferred over the crosslinked network for preparing transparent parts because uncrosslinked polymers tend to phase separate over time (kinetically limited), except in rare cases of compatibility between the two or more polymeric phases. Mixtures containing only mono-functional reactive plasticizers will often react slightly with the dead polymer chains (even when no crosslinkable side groups are present on the dead polymer), desirably producing a slightly crosslinked network having sufficient stability to prevent phase separation over time periods of interest. When a non-transparent finished part is the objective, then the above limitations are relieved.
The invention further encompasses certain semi-solid-like polymerizable compositions useful with the process. The semi-solid compositions comprise a mixture of a reactive plasticizer, an initiator and, optionally, a dead polymer. The compositions may optionally include other additives well-known in the art to effect mold release, improved stability or weatherability, non-yellowing properties, and the like.
This invention permits a broad selection of reaction chemistries to achieve precision parts with the required mechanical, thermal, optical and other desired properties. It obtains precision parts that are stress-free and flawless, with little or no birefringence. Precision products can be manufactured that are very impact-resistant or that have a prismatic geometry, or have other desirable but previously difficult-to-achieve characteristics.
The terms xe2x80x9caxe2x80x9d and xe2x80x9canxe2x80x9d, as used herein and in the appended claims mean xe2x80x9cone or morexe2x80x9d.
The term xe2x80x9cdead polymerxe2x80x9d as used herein and in the appended claims refers to a fully polymerized, generally non-reactive polymer. When certain polymer chemistries are used, the dead polymer may react with a reactive plasticizer, even if the dead polymer does not have unsaturated entities within or attached to the chain. The dead polymer may be linear or branched, homopolymer or copolymer. In the case of a copolymer, the sequence distribution may be random in sequence or blocky. The block copolymers may be tapered, or may have grafted side chains. The architecture of the dead polymer may be branched, multi-chain, comb-shaped or star-shaped, either symmetrical or non-symmetrical. Di-block, tri-block or multi-block structures all fall within the scope of this invention.
The semi-solid polymerizable composition useful in the production of precision parts is prepared, in one embodiment, by mixing the dead polymer with at least one small-molecule species, which is itself polymerizable or crosslinkable. This small-molecule species is referred to herein and in the appended claims as a xe2x80x9creactive plasticizerxe2x80x9d. In another embodiment, the semi-solid polymerizable core composition comprises a reactive plasticizer or a mixture of reactive plasticizers, without the presence of a dead polymer. The reactive plasticizer may encompass monomers, crosslinkers, oligomeric reactants, oligomeric crosslinkers, or macromeric reactants or macromeric crosslinkers (collectively macromers). The reactive plasticizer plasticizes the dead polymer to give a composition having the desired consistency at ambient temperature or below (i.e., able to maintain a shape for easy handling over short time periods), and at the processing temperature (i.e., malleable enough to be compressed or formed into a desired shape). The said processing temperature can be chosen conveniently to be moderately above or below ambient temperature. The reactive plasticizers can be mixtures themselves, composed of mono-functional, bi-functional, tri-functional or other homogeneous or heterogeneous multi-functional entities (heterogeneous reactive plasticizers being those that possess two or more different types of reactive functionalities).
In total, the amount and composition of the reactive plasticizer in the resulting formulation are such that the formulation is semi-solid-like and can be effectively handled with no need for a gasket in the mold. That is, the reactive plasticizer is present in concentrations sufficient to allow malleability and moldability at the desired processing temperature and pressure; however, the mixture is non-dripping and not free-flowing over short time periods at the material storage temperature and mold closure temperature, which can be conveniently chosen to be at ambient temperatures, or slightly above or below. The amount of reactive plasticizer is generally about 0.1% to about 100% by weight, preferably from about 1% to about 50%, more preferably from about 3% to about 25%.
The types and relative amounts of reactive plasticizer and dead polymer will dictate the time and temperature-dependent visco-elastic properties of the mixture. The visco-elastic properties of the chosen compositions may be wide and varied. For the practice of the invention as disclosed herewith, it is only required that the composition be highly viscous, semi-solid or solid-like for handling and/or insertion into a mold assembly at some temperature, while being semi-solid or liquid-like (i.e., deformable) at the processing temperature to which the mold assembly is heated or cooled after closure. Since virtually all known material systems become more compliant upon heating, the molding temperature will usually, but not necessarily, be equal to or higher than the handling temperature. In principle, any reactive plasticizer system (with or without dead polymer) which can be handled as a semi-solid or solid at some temperature, and which can be made to conform to a desired geometry (with or without changing the temperature and/or using force), can be used for the practice of the invention.
If the mixture consists mostly or wholly of reactive plasticizers, it may need to be cooled or partially cured in order to achieve the semi-solid-like consistency desirable for handling. Likewise, the mold-assembly temperature (the temperature at which the semi-solid composition is inserted into the mold) may desirably be below ambient temperature to prevent dripping or leaking from the mold prior to closure. Once the mold is closed, however, it may be compressed and heated to any pressure and temperature desired to induce conformation of the material to the internal mold cavity, even if such temperatures and pressures effect a free-flowing composition within the mold cavity (i.e., a composition which becomes free-flowing at the molding temperature is not precluded, and may be desirably chosen for the molding of fine-featured parts in which the molding compound must fill in small cavities, channels, and the like).
Alternatively, the dead polymer and reactive plasticizer mixture may be chosen and mixed in such proportions so as to form a composition that is glassy and rigid at ambient temperatures. Such a material will have all the benefits of ease of handling as a semi-solid composition, and will only require that the mold temperature after closure be adjusted to the softening temperature of the mixture in order to allow sufficient deformation of the material so that it may assume the desired shape (optionally in conjunction with applied pressure).
The composition most desirable for the practice of the invention will typically consist of about 3% to about 25% of a reactive plasticizer in a dead polymer. Once combined, said preferable mixture should provide a composition that is semi-solid at room temperature, such that it may be easily handled as a discrete part or object without undue stickiness or deformability. The mixture may be more easily homogenized at an elevated temperature and discharged into discrete parts which roughly approximate the desired shape of the final object, then cooled for handling or storage. When said preferable mixture or parts are placed into a mold and heated slightly above ambient temperature, or otherwise shaped or compressed while simultaneously heated, they will deform into the desired geometry without undue resistance. Such a composition is preferable in that handling and storage may occur at room temperature, while molding or shaping into the desired geometry may occur at temperatures only slightly or moderately removed from ambient. This and other benefits of the invention will be disclosed in more detail herewith.
When used without a dead polymer or with only a small amount of dead polymer, the reactive plasticizer should be a reactive oligomer or a reactive short polymer, having at least one reactive functional group. In this case, the reactive plasticizer should be a longer chain molecule, of from about 1 to about 1000 repeat units, and preferably between about 1 and about 100 repeat units. These reactive plasticizers (or mixture of reactive plasticizers) have a high viscosity, preferably of greater than 1000 centipoise, at the temperature at which the material is to be handled (e.g., inserted into a mold cavity) to exhibit semi-solid behavior. In the case of low molecular weight reactive plasticizers, the mixture may first be slightly polymerized to create the semi-solid consistency required for downstream processing as disclosed in this invention. Alternatively, the mixture may be cooled to create the semi-solid consistency.
Polymerization initiators are added to the mixture to trigger polymerization after molding. Such initiators are well-known in the art. Optionally, other additives may be added, such as mold release agents to facilitate removal of the object from the mold after curing, non-reactive conventional plasticizers or flexibilizers, pigments, dyes, organic or inorganic fibrous or particulate reinforcing or extending fillers, thixotropic agents, indicators, inhibitors or stabilizers (weathering or non-yellowing agents), UV absorbers, surfactants, flow aids, chain transfer agents, and the like. The initiator and other optional additives may be dissolved in the reactive plasticizer component prior to combining with the dead polymer to facilitate complete dissolution into and uniform mixing with the dead polymer. Alternatively, the initiator and other optional additives may be added to the mixture just prior to polymerization, which may be preferred when thermal initiators are used.
The ingredients in the semi-solid polymerizing mixture can be blended by hand or by mechanical mixing. The ingredients can preferably be warmed slightly to soften the dead polymer component. Any suitable mixing device may be used to mechanically homogenize the mixture, such as blenders, kneaders, extruders, mills, in-line mixers, static mixers, and the like, optionally blended at temperatures above ambient temperature, or optionally blended at pressures above or below atmospheric pressure.
In one presently preferred embodiment of the invention, an optional waiting period may be allowed during which the ingredients are not mechanically agitated. The optional waiting period may take place between the time the ingredients are initially metered into a holding container and the time at which they are homogenized mechanically or manually. Alternatively, the ingredients may be metered into a mixing device, said mixing device operated for a sufficient period to dry-blend the ingredients, then an optional waiting period may ensue before further mixing takes place. The waiting period may extend for an hour to one or more days. The waiting period may be chosen empirically and without undue experimentation as the period that gives the most efficient overall mixing process in terms of energy consumption. This embodiment of the invention may be particularly beneficial when the polymerizable mixture contains a high fraction of the dead polymer ingredient, especially when the dead polymer is glassy or rigid at ambient temperatures. Utilization of a waiting period may also be particularly beneficial when the dead polymer is thermally sensitive and so cannot be processed over an extended time at temperatures above its softening point without undue degradation, or when one or more of the reactive plasticizers is particularly volatile and so cannot be easily mixed with a high-melting-temperature polymer without undue evaporative loss of the reactive plasticizer.
By xe2x80x9csemi-solidxe2x80x9d and xe2x80x9csemi-solid-likexe2x80x9d are meant that, in essence, the polymerizable composition is a rubbery, taffy-like mass at sub-ambient, ambient, or elevated temperatures. Preferably the semi-solid mass has a sufficiently high viscosity to prevent dripping at ambient temperatures and pressures or below, but is malleable and can easily deform and conform to mold surfaces if the mold cavity is slightly heated or as a result of pressure exerted by pressing the two mold halves together, or a combination of both heat and pressure. The advantage of this semi-solid composition is that it can be pre-formed into a slab, disk, ball, or sheet, for example, which may in turn pressed between mold halves to define a lens or other object without an intervening gasket. Alternatively, a glob of this composition can be applied at slightly elevated temperature on one side of a mold cavity. The other mold half is then brought into contact with the semi-solidified mass, which is squeezed into the final desired shape by the approaching mold halves. Again, there is no need for gasketing of the mold halves, as the composition will not run out of the mold due to its viscous semi-solid-like nature (except that which is squeezed out in clamping the mold shut). Furthermore, the shaped mass may be kept at a slightly elevated temperature after mold closure to anneal away the stresses (birefringence), if any, introduced by squeezing, before the system is exposed to a source of polymerizing energy (such as UV light or temperature) to trigger network formation (curing).
With or without the annealing step, the assembly (i.e., the front mold, the rubbery precursor polymerizable composition, and the back mold) can then be exposed to UV or heat or another polymerizing energy source to complete polymerization of the reactive plasticizers in the mixture. The reactive plasticizers set up a semi-interpenetrating polymer network within an entangled dead polymer network. In some cases, the reactive plasticizer may react with groups on the dead polymer chain to form completely crosslinked networks. Optimization of engineering properties can be accomplished by the judicious quantitation of the architecture of the reactive molecules, their concentration and composition.
In case the edges of the finished parts require dimensional precision, then a precisely matched (or measured) amount of the reaction glob (mass) must be used. The front and back mold halves can be fashioned in such a way as to allow precise telescopic fit of one within the other. In one embodiment of this invention, the semi-solid material may be placed in about the center of the mold so that when the molds are compressed together, the semi-solid will flow radially outward towards the mold edges. Such a configuration allows the semi-solid material to fill in the gap between the mold while reducing or eliminating the entrainment of bubbles, air pockets, or other void defects. During mold closure, excess material (if any) can overflow the tiny annular region and be easily trimmed off after cure. If the amount of mass discharged into the mold cavity is measured very precisely, such flash can be eliminated altogether for repetitive production of identical finished objects. Alternatively, the molds may be designed so that the compressed semi-solid material only fills in part of the mold cavity, leaving the outer edges unfilled for example. In any case, the separation distance between the molds may be easily monitored so as to control the thickness of the molded part. Part thicknesses may easily range from microns to tens of centimeters with virtually no change in processing conditions or material formulations.
If the reactive plasticizers can be designed to conservatively exhibit a total shrinkage in the neighborhood of 8% when cured in their pure state, then a mixture containing less than 50% of such plasticizers in dead polymers will give only a very small (less than 4%) total shrinkage, assuming linear property additivity. This amount of total shrinkage is manageable by most curing regimens, including blanket UV exposure (for photo-cure) and rapid temperature spikes (for thermal-cure). In certain realistic cases, the intrinsic shrinkage of oligomeric reactive plasticizers may be about 5%, yet the maximum amount used in the formulation for plasticization may be only 10% by weight, giving rise to a system than shrinks approximately 0.5%. In certain other realistic cases, the intrinsic shrinkage of small molecule reactive plasticizers may be about 10%, yet the maximum amount used in the formulation for plasticization may be only 5% by weight, again giving rise to a system than shrinks approximately 0.5%.
Even in the case where 50-100% reactive plasticizers are present, low shrinkage may be realized because the system is not now limited to non-viscous, flowable components. In the prior art, material systems were limited by low-viscosity requirements, which inherently translates to systems possessing a high population of reactive entities and therefore exhibiting large shrinkage upon cure. Because low viscosity is no longer a requirement with the practice of the present invention, semi-solid material systems with high viscosity, optionally high molecular weight, and inherently low shrinkage may now be utilized.
The molding compositions of the invention thus display low shrinkage upon cure. By xe2x80x9clow shrinkagexe2x80x9d is meant that the shrinkage of the composition of the invention upon cure will typically be less than about 5%, preferably less than about 2%. This benefit enables molding processes in which the fabricated part shows high replication fidelity of the mold cavity. That is, because shrinkage of the polymerizable formulation is quite small (typically less than 5%, more preferably less than 2%), the cured part will retain the shape of the mold cavity throughout cure. Problems associated with shrinkage such as premature mold release, which greatly hinder and complicate current state-of-the-art practices, are eliminated. Note that the present invention can also be practiced with other types of polymerizable systems, such as those initiated with ionic initiators, microwaves, x-rays, e-beams, or gamma radiation. In addition, condensation, ring-opening and other polymerization mechanisms may be similarly practiced.
The high replication fidelity achieved with the invention disclosed herewith may be appreciated in the casting of optical components which rely on precise, smooth surfaces such as ophthalmic lenses, contact lenses, prisms, optical disks and the like. High fidelity replication may be also appreciated in the molding of components that rely on surfaces having desired exact topographies, such as optical storage disks, printing plates or other pattern transfer media. High replication fidelity may be further appreciated in the molding of three dimensional or complex geometry components which require dimensionally precise replication from the mold such as couplers, housings, gears, various packaging assemblies, and the like.
It should be appreciated that the cross-linked interpenetrating polymer networks formed during the practice of the invention disclosed herewith provide continued dimensional precision during the use or operation of the molded part (i.e., dimensional stability). That is, the cross-linked networks do not flow when heated above their glass transition temperature, and provide improved resistance to chemical attack, repeated load cycles, and the like. The benefits of dimensional stability achieved with the practice of the invention will be appreciated by fabricators of all types of moldable objects which may benefit from precise geometries.
Another beneficial characteristic of the present invention is that free radical polymerization and other triggerable chain polymerization mechanisms (e.g., via the use of ionic initiators) proceed efficiently in semi-solid media because of reduced oxygen inhibition and slow termination reactions. Without being bound by theory, this is believed to be due in part to the decreased mobility of oxygen molecules in high-viscosity media. In addition, oxygen-scavenging additives may be incorporated into the polymerizable mixture prior to initiation of cure. Thus, semi-solid polymerizable mixtures allow processing in which the need for nitrogen purging during mixing and molding steps is reduced. Curing reactions will also proceed further to completion in the near-surface region of the object even when oxygen is present in the gas phase surrounding the object to be cured, thus reducing or eliminating the need for oxygen barrier layers at the surface of the molded part. UV initiators may further be chosen and incorporated in such concentrations so as to give rapid curing using UV-triggered polymerizations. By xe2x80x9crapid curingxe2x80x9d is meant that the molded object may be substantially cured by UV light within about 1 hour, or as fast as a few minutes. Such curing regimens provide significantly faster curing cycles than the 8- to 24-hour curing cycle times typical in the current art.
Yet another beneficial characteristic of the disclosed invention is that thermal spikes produced by the polymerization of unsaturated species are mitigated. Conventional casting processes utilize low-viscosity systems, which contain near 100% reactive components. Such systems experience temperature spikes due to the exothermic curing reaction. When the entire part is irradiated and cured at once, part temperatures can increase rapidly by up to 200xc2x0 C. over the part temperature prior to cure initiation due to the curing exotherm. Such temperature excursions lead to thermal degradation, discoloration, and part warpage upon being released from the mold due to thermal expansion-contraction effects.
The semi-solid-like nature of the polymerization mixture of this invention disclosed here greatly reduces such temperature spikes because the proportion of reactive components in the system is typically less than 50% by weight, and preferably less than 25% by weight, thereby substantially reducing the exotherm during cure. Thus, a mixture with only 25% by weight of the reactive plasticizer component will rise at most approximately 50xc2x0 C. Such temperature rises are easily withstood by most material formulations, and further, such a small temperature excursion precludes part warpage after mold release. Even when the amount of reactive plasticizer is above 50%, the semi-solid compositions will typically possess a low population of reactive entities, thus mitigating high temperature excursions and associated problems. Reduced exotherms will be appreciated by fabricators of precise, moldable objects, especially when parts containing thermally-sensitive constituents, or those having thick cross sections are to be fabricated.
This process enjoys the benefits of (1) material formulation flexibility, (2) finished parts being thermosets with interpenetrating networks or slightly crosslinked networks, (3) room temperature or slightly elevated temperature processing, (4) UV curing (photo-polymerization) that is not limited by heat transfer time or long cycle time, (5) rapid, efficient, low-oxygen-inhibited polymerization carried out in semi-solid media, (6) minimal temperature rise due to exothermic reactions, (7) low pressure operation, and (8) either continuous process or batch-wise operation with an intermediate step of casting from pre-forms (e.g., disks, slabs, balls, or pucks).
Two example process schemes are discussed below. Numerous variants can be envisioned by those skilled in the art of polymerization reaction engineering and polymer processing and molding. Hence, the present invention is not limited by these two example processing embodiments.
Batchwise processing provides precision-casting from pre-forms. A dead polymer, a reactive plasticizer, and an initiator package (optionally including other additives such as anti-oxidants, stabilizers, and the like) are mixed together (optionally with a waiting period during which the ingredients are not mechanically agitated) in a mixer equipped with temperature control and vacuum capabilities, to form a semi-solid polymerizable composition free of voids or air bubbles. The semi-solid composition is discharged from the mixer, and the discharge is cast into slabs (disks, pucks, balls, buttons, sheets, and the like), which serve as pre-forms for the subsequent precision casting operation. Alternatively, an extruded strand of the semi-solid composition can be sliced or diced into pre-forms. In a downstream operation, the pre-forms (which may be stored at room temperature or refrigerated temperatures in the interim, or which may even be partially cured to facilitate handling and storage) can be retrieved and shaped into the desired geometry for production of the final article. In a presently preferred embodiment, the pre-forms are placed in about the center of and sandwiched between two mold halves, whereupon the mold is closed, briefly heated to enhance material compliance as necessary, and flood-exposed by UV- or heat-cured. One can envision this processing scheme to suit just-in-time production situations, where an inventory of pre-forms can be used to make precise parts upon demand. In situations where a large variety of parts must be made just-in-time, this approach offers great ease of material handling. Eye glass lenses or contact lenses having a large range of prescriptions constitute one such example where this batchwise process scheme is appropriate.
In an alternative, continuous process, the dead polymer, the reactive plasticizer, and the initiator package (optionally including other additives such as anti-oxidants, stabilizers, and the like) are mixed together in an extruder. There is optionally a waiting period prior to the material being introduced into the extruder, during which time the ingredients are in intimate contact with one another, but are not mechanically agitated. Periodically, the extruder discharges a fixed amount of semi-solid reactive plasticizer-dead polymer composition as a warm glob into approximately the center of a temperature-controlled mold cavity (or in such other manner that voids, bubbles, weld lines, and the like are minimized during the molding process). The mold, which exhibits a telescopic fit of the front/back mold assembly, is then closed. An optional waiting period may ensue at the still-elevated temperature to anneal any stresses induced by squeezing of the glob. Finally, the captured material is flood-exposed by UV or heat-cured. This second example process flow is best suited for situations where the number of different parts is small, but each part is mass manufactured into many copies. Precision optics constitute one potential application area, as well as many engineering parts with intricate geometries found in sporting goods, automotive, construction and aerospace, etc., industries.
There exist in the literature at least four basic ways to develop a new polymer system with unique properties: (1) synthesize new monomers, (2) develop new methods and techniques of polymerization, (3) combine known monomers/crosslinkers in such a way that the resulting material has superior attributes, and (4) combine known polymers into blends or alloys. In the present invention, we concentrate on a fifth, new approach, i.e., the combination of dead polymers with monomeric or oligomeric reactive diluents. These reactive diluents, when used in small amounts, actually serve the role of plasticizers. Instead of inert plasticizers that simply remain in a plastic to soften the material, the reactive diluents/plasticizers can initially soften the polymer to facilitate the molding process (allowing for lower temperature molding processes compared with the processing of conventional, unplasticized thermoplastic materials); but, upon curing, the polymerized reactive plasticizers lock in the precise shape and morphology of the polymer within the cured resin (and also lock in the reactive plasticizers themselves so that they cannot leak or be leached out of the resin over time).
Once polymerized, the reacted plasticizers typically no longer soften the dead polymer to the same extent as before curing. The hardness of the cured resin will be determined by the chemical structure and functionality of the reactive plasticizers and dead polymers used, their concentration, molecular weight, and the degree of crosslinking and grafting to the dead polymer chains. Additionally, chain terminating agents can be added to the formulation prior to polymerization in order to limit the molecular weight and degree of crosslinking of the polymer formed by reacting the plasticizers, thus adding a measure of control in altering the final mechanical properties of the cured parts. At the same time polymerization results in no significant shrinkage (due to the overall low concentration of the reactive plasticizer or the low population of reactive entities), so the finished objects remain dimensionally stable, yielding high fidelity replication of the mold cavity. Precise geometric replication of the mold cavity is further preserved due to the relatively low molding temperatures and reduced exotherm from polymerization, which is particularly applicable to part designs having thick cross-sections.
Subsequent discussions concerning the basic material design considerations are divided into two categories based on the type of dead polymer utilized in the process. One category begins with standard thermoplastics as the dead polymer. These include, but are not limited to, polystyrene, polymethylmethacrylate, poly(acrylonitrile-butadiene-styrene), polyvinyl chloride, polycarbonate, polysulfone, polyvinylpyrrolidone, polycaprolactone, and polyetherimide, for example. The thermoplastics may optionally have small amounts of reactive entities attached (copolymerized, grafted, or otherwise incorporated) to the polymer backbone to promote crosslinking upon cure. They may be amorphous or crystalline. They may be classified as high performance engineering thermoplastics (e.g., polyether imides, polysulfones, polyether ketones, etc.), or they may be biodegradable (starch, prolamine, and cellulose, for example). These examples are not meant to limit the scope of compositions possible during the practice of the current invention, but merely to illustrate the broad selection of thermoplastic chemistries permitted under the present disclosure. Reactive plasticizers may be mixed with a thermoplastic polymer such as those listed above to give a semi-solid-like composition that can be easily molded into dimensionally precise objects. Upon polymerizing to form a cured resin, the dimensional stability of the object is locked in to give exact three-dimensional shapes or precise surface features. Thermoplastic polymers may be chosen in order to give optical clarity, high index of refraction, low birefringence, exceptional impact resistance, good thermal stability, high oxygen permeability, UV transparency or blocking, low cost, or a combination of these properties in the finished, molded object.
The other category utilizes xe2x80x9cthermoplastic elastomersxe2x80x9d as the dead polymer. An exemplary thermoplastic elastomer is a tri-block copolymer of the general structure xe2x80x9cA-B-Axe2x80x9d, where A is a thermoplastic rigid polymer (i.e., having a glass transition temperature above ambient) and B is an elastomeric (rubbery) polymer (glass transition temperature below ambient). In the pure state, ABA forms a microphase-separated morphology. This morphology consists of rigid glassy polymer regions (A) connected and surrounded by rubbery chains (B), or occlusions of the rubbery phase (B) surrounded by a glassy (A) continuous phase, depending on the relative amounts of (A) and (B) in the polymer. Under certain compositional and processing conditions, the morphology is such that the relevant domain size is smaller than the wavelength of visible light. Hence, parts made of such ABA copolymers can be transparent or at worst translucent. Thermoplastic elastomers, without vulcanization, have rubber-like properties similar to those of conventional rubber vulcanizates, but flow as thermoplastics at temperatures above the glass transition point of the glassy polymer region. Melt behavior with respect to shear and elongation is similar to that of conventional thermoplastics. Commercially important thermoplastic elastomers are exemplified by SBS, SIS, and SEBS, where S is polystyrene and B is polybutadiene, I is polyisoprene, and EB is ethylenebutylene copolymer. Many other di-block or tri-block candidates are known, such as poly(aromatic amide)-siloxane, polyimide-siloxane, and polyurethanes. SBS and hydrogenated SBS (i.e., SEBS) are well-known products from Shell Chemicals (Kraton(copyright)). DuPont""s Lycra(copyright) is also a block copolymer.
When thermoplastic elastomers are chosen as the starting dead polymer for formulation, exceptionally impact-resistant parts may be manufactured by mixing with reactive plasticizers. The thermoplastic elastomers, by themselves, are not chemically crosslinked and require relatively high-temperature processing steps for molding which, upon cooling, leads to dimensionally unstable, shrunken or warped parts. The reactive plasticizers, if cured by themselves, may be chosen to form a relatively glassy, rigid network, or may be chosen to form a relatively soft, rubbery network, but with relatively high shrinkage. When thermoplastic elastomers and reactive plasticizers are blended together and reacted to form a cured resin, they form flexible networks with superior shock-absorbing and impact-resistant properties. By xe2x80x9cimpact-resistantxe2x80x9d is meant resistance to fracture or shattering upon being struck by an incident object. Depending on the nature of the dead polymer and reactive plasticizers used in the formulation, the final cured resin may be more stiff or more stretchy than the starting dead polymer. Composite articles exhibiting exceptional toughness may be fabricated by using a thermoplastic elastomer which itself contains polymerizable groups along the polymer chain, such as SBS tri-block copolymers, for example.
Furthermore, when compatible systems are identified, transparent objects can be cast. xe2x80x9cCompatibilityxe2x80x9d refers to the thermodynamic state where the dead polymer is solvated by the reactive plasticizers. Hence, molecular segments with structural similarity would promote mutual dissolution. Aromatic moieties on the polymer generally dissolve in aromatic plasticizers, and vice versa. Hydrophilicity and hydrophobicity are additional considerations in choosing the reactive plasticizers to mix with a given dead polymer. Even when only partial compatibility is observed at room temperature, the mixture often becomes uniform at a slightly increased temperature; i.e., many systems become clear at slightly elevated temperatures. Such temperatures may be slightly above ambient temperatures or may extend up to the vicinity of 100xc2x0 C. In such cases, the reactive components can be quickly cured at the elevated temperature to xe2x80x9clock-inxe2x80x9d the compatible morphology in the cured resin before system cool-down. Hence, both material and processing approaches can be exploited to produce optically clear parts. Optically clear and dimensionally exact parts have a wide range of potential applications. Both polycarbonate and thermoplastic elastomers can be employed to create useful formulations by mixing with suitable reactive plasticizer packages. With the process innovation described herewith, powerful new material systems can be developed.
A preferred formulation for developing optically clear and high impact-resistant materials uses styrene-rich SBS tri-block copolymers that contain up to about 75% styrene. These SBS copolymers are commercially available from Shell Chemicals (Kraton(copyright)), Phillips Chemical Company (K-Resin(copyright)), BASF (Styrolux(copyright)), Fina Chemicals (Finaclear(copyright)), and Asahi Chemical (Asaflex(copyright)). In addition to high impact resistance and good optical clarity, such styrene-rich copolymers yield materials systems which preferably exhibit other desirable properties such as a relatively high refractive index (that is, the index of refraction is equal to or greater than about 1.54) and low density (their densities are less than about 1.2 g/cc, and more typically are about 1.0 g/cc).
When the mixture refractive index is an especially important consideration, high refractive index polymers may be used as one or more of the dead-polymer components. Examples of such polymers include polycarbonates and halogenated polycarbonates, polystyrenes and halogenated polystyrenes, polystyrene-polybutadiene block copolymers and their hydrogenated and halogenated versions (all of which may be linear, branched, star-shaped, or non-symmetrically branched or star-shaped), polystyrene-polyisoprene block copolymers and their hydrodrogenated and halogenated versions (including the linear, branched, star-shaped, and non-symmetrical branched and star-shaped variations), poly(pentabromophenyl (meth)acrylate), polyvinyl carbazole, polyvinyl naphthalene, poly vinyl biphenyl, polynaphthyl (meth)acrylate, polyvinyl thiophene, polysulfones, polyphenylene sulfides, urea-, phenol-, or naphthyl-formaldehyde resins, polyvinyl phenol, chlorinated or brominated polystyrenes, poly(phenyl xcex1- or xcex2-bromoacrylate), polyvinylidene chloride or bromide, and the like. In general, increasing the aromatic content and the halogen content (especially bromine) are effective means well-known in the art for increasing the refractive index of a material. These properties are especially preferred for ophthalmic lenses as it enables the production of ultra thin, light-weight eyeglass lenses which are desirable for low-profile appearances and comfort of the wearer.
Alternatively, elastomers, thermosets (e.g., epoxies, melamines, acrylated epoxies, acrylated urethanes, etc., in their uncured state), and other non-thermoplastic polymeric compositions may be desirably utilized during the practice of this invention.
Mixtures of such materials may also be beneficially used to create dimensionally stable parts with desirable properties. For example, impact modifiers may be blended into various thermoplastics or thermoplastic elastomers to improve the impact strength of the final cured resin. In such cases, the presence of the reactive plasticizers will facilitate blending by lowering the softening temperature of the polymers to be blended. This is especially beneficial when a temperature-sensitive material is being blended with a high-Tg polymer. When optically clear materials are desired, the mixture components may be chosen to have the same refractive index (iso-refractive) such that light scattering is reduced. When iso-refractive components are not available, the reactive plasticizers may also help reduce the domain size between two immiscible polymers to below the wavelength of light, thus producing an optically clear polymer mixture which would have otherwise been opaque.
The reactive diluents (plasticizers) can be used singly or, alternatively, mixtures can be used to facilitate dissolution of a given dead polymer. The reactive functional group can be acrylate, methacrylate, acrylic anhydride, acrylamide, vinyl, vinyl ether, vinyl ester, vinyl halide, vinyl silane, vinyl siloxane, (meth)acrylated silicones, vinyl heterocycles, diene, allyl and the like. Other less known but polymerizable functional groups can be investigated, such as epoxies (with hardeners) and urethanes (reaction between isocyanates and alcohols). In principle, any monomers may be used as reactive plasticizers in accordance with the present invention, although preference is given to those which exist as liquids at ambient temperatures or slightly above, and which polymerize readily with the application of a source of polymerizing energy such as light or heat in the presence of a suitable initiator.
Reactive monomers, oligomers, and crosslinkers that contain acrylate or methacrylate functional groups are well known and commercially available from Sartomer, Radcure and Henkel. Similarly, vinyl ethers are commercially available from Allied Signal. Radcure also supplies UV curable cycloaliphatic epoxy resins. Photo-initiators such as the Irgacure and Darocur series are well-known and commercially available from Ciba Geigy, as is the Esacure series from Sartomer. Thermal initiators such as azobisisobutyronitrile (AIBN), benzoyl peroxide, dicumyl peroxide, t-butyl hydroperoxide, and potassium persulfate are also well known and are available from chemical suppliers such as Aldrich. Vinyl, diene, and allyl compounds are available from a large number of chemical suppliers, as is benzophenone. For a reference on initiators, see, for example, Polymer Handbook, J. Brandrup, E. H. Immergut, eds., 3rd Ed., Wiley, New York, 1989. Below we will use acrylates (and in a few cases, methacrylates) to illustrate the flexibility of our formulation approach. Similar structures with other reactive groups based on either small or large molecule architectures (such as acrylamides, vinyl ethers, vinyls, dienes, and the like) can be used in conjunction with the disclosed casting process.
The compatibility of dead polymer-reactive plasticizer mixtures is demonstrated by checking the optical transparency of the resulting material at room temperature or slightly above, as illustrated by Example 1 below. To demonstrate the great diversity of reactive plasticizers that can be used to achieve such compatibility, we will name only a few from a list of hundreds to thousands of commercially available compounds. For example, mono-functional entities include, but are not limited to: isodecyl acrylate, hexadecyl acrylate, stearyl acrylate, isobornyl acrylate, vinyl benzoate, tetrahydrofurfuryl acrylate (or methacrylate), caprolactone acrylate, cyclohexyl acrylate, methyl methacrylate, ethyl acrylate, propyl acrylate, and butyl acrylate, etc. Bi-functional entities include, but are not limited to: polyethyleneglycol diacrylate, polypropyleneglycol diacrylate, hexanediol diacrylate, Photomer 4200 (from Henkel), polybutadiene diacrylate (or dimethacrylate), Ebecryl 8402 (from Radcure), bisphenol A diacrylate, ethoxylated (or propoxylated) bisphenol A diacrylate. Tri-functional and multi-functional entities include, but are not limited to: trimethylolpropane triacrylate (and its ethoxylated or propoxylated derivatives), pentaerythritol tetraacrylate (and its ethoxylated or propoxylated derivatives), Photomer 6173 (a proprietary acrylated oligomer of multi functionality, from Henkel), and a whole host of aliphatic and aromatic acrylated oligomers from Sartomer (the SR series), Radcure (the Ebecryl series), and Henkel (the Photomer series).
When high refractive index materials are desired, the reactive plasticizers may be chosen accordingly to have high refractive indices. Examples of such reactive plasticizers, in addition to those mentioned above, include brominated or chlorinated phenyl (meth)acrylates (e.g., pentabromo methacrylate, tribromo acrylate, etc.), brominated or chlorinated naphthyl or biphenyl (meth)acrylates, brominated or chlorinated styrenes, tribromoneopentyl (meth)acrylate, vinyl naphthylene, vinyl biphenyl, vinyl phenol, vinyl carbazole, vinyl bromide or chloride, vinylidene bromide or chloride, bromoethyl (meth)acrylate, bromophenyl isocyanate, and the like.

Near-net-shape polymerization process and materials suitable for use therewith


The present invention is directed to an optical switch for switching the light from one of a plurality of inputs to one of a plurality of outputs. The switch contains at least two moveable mirrors constructed using MEM technology. These switches are useful in applications such as fiber-fiber switches and optical disk drives. The switches may be combined with other optical equipment including stationary mirrors and lenses.

The present invention generally relates to optical switches and, in particular, to optical switches for use in optical disk drive systems.
Current optical switches, such as fiber to fiber switches, use various mechanisms to switch light beams from an input to a selected output. For instance, piezoelectric actuators are used to move fibers in the focal plane of lenses to create a directional optical transmitter or receiver. Alternatively, the fiber is held in a fixed position in the center of the focal plane of the lens and the beam is directed to the desired location with one or more movable mirrors. The output of the beam is determined by controlling the mirrors within the switch. Optical switches can be used to switch light in various applications including fiber to fiber switches and in multi-disk optical disk drives.
In the case of optical disk drives, optical switches can be used to direct a beam of light from a single light source to any one of a number of optical disks. In general, various optical disk drive systems have been proposed for use with multiple optical disks loaded on a rotationally mounted spindle, and such systems have become increasingly popular because of their large storage capabilities. A typical optical disk drive system uses one or more laser sources to transmit a laser beam onto a selected track of an optical disk. In reading applications, the beam reflected from the surface of the optical disk is monitored by a signal detector to reconstruct information stored on the recording surfaces of disks.
Some of the existing multiple disk drive systems use a single head assembly mounted on an elevator carriage, which physically moves within the drive to bring the laser beam to each reflective disk surface. Some of the existing multiple disk drive systems use a multiple head assembly system, where one head assembly is assigned to each of reflective surfaces of the optical disks. Others, such as disclosed in U.S. Pat. No. 5,153,870 to Lee et al., provide a rotary head actuator which employs an optically switchable reflector using removable index matching fluid to distribute a laser beam from a laser source to one of several optical disks.
These prior art storage devices suffer from various disadvantages. For example, one problem associated with some of the known storage devices is that additional access time is required during positioning of the laser beam between optical disks. This problem is more prevalent when the requested data is dispersed among multiple disk surfaces. Some storage devices are expensive to manufacture and cumbersome to fit into small cases since each head assembly contains a complete set of optical head components, including laser beam source, detector, mirrors and lenses.
The present invention is directed to an optical switch for switching a light beam from at least one optical input to one of a plurality of outputs. The optical switch includes a first movable mirror for reflecting the light beam from the optical input and a second movable mirror for reflecting the light beam reflected from the first movable mirror, wherein the first movable mirror is adjusted to guide the light beam from the optical input to a selected point on the second movable mirror, and the second movable mirror is adjusted to guide the light beam from the first movable mirror to one of the outputs.
In the optical switch of the present invention, the first and second movable mirrors are rotatable about at least one pivot axis, and the optical switch further includes a control mechanism to control the rotation of the first and second moveable mirrors about the pivot axis. In one embodiment of the present invention, the first and second moveable mirrors are rotatable about both a first pivot axis and a second pivot axis, and the optical switch further includes a control mechanism to control the rotation of the first and second moveable mirrors about both axes.
In another embodiment, the optical switch includes a plurality of optical inputs, and the first movable mirror is adjusted to guide the light beam emitted from one of these plurality of optical inputs to a selected point on the second movable mirror.
In one embodiment of the present invention, the mirror, includes a top reflective surface, a bottom surface opposite the top surface, a magnetic material attached to at least a portion of the bottom surface, and at least one magnetic coil for attracting the magnetic material to rotate the moveable mirrors. In another embodiment, the moveable mirrors also include a support frame, a gimbal frame rotatably connected to the support frame, and a mirror portion rotatably connected to the gimbal frame, wherein the mirror is rotatable about a first axis of rotation and the gimbal frame is rotatable about a second axis of rotation.
In yet another embodiment of the optical switch, the mirror portion further includes a top reflective surface and a bottom surface opposite the top surface, and the optical switch also includes a magnetic material attached to at least a portion of the bottom surface of the mirror portion and at least a portion of the gimbal frame. A first set of magnetic coils for attracting the magnetic material attached to the mirror portion is positioned adjacent to the magnetic material on the mirror portion to rotate the mirror about the first axis of rotation, and a second set of magnetic coils is positioned adjacent to the magnetic material on the gimbal frame for attracting the magnetic material on the gimbal frame to rotate the mirror about the second axis of rotation. A wing structure can be attached non-rotatably to the mirror portion, and the magnetic material attached to the wing structure.
The optical switch of the present invention can also include a damping material disposed between the magnetic material and the magnetic coils. Suitable materials for the dampening material include aluminum and copper. The magnetic coils are electromagnets. The magnetic material can be a permanent magnet that is polarized in a direction perpendicular to the bottom surface or in a direction parallel to the bottom surface.
The present invention is also directed to an adjustable mirror assembly having a support base, a mirror having a reflective surface and connected to the support base by a first flexible pivot, and two linear actuators connected to the mirror by a second flexible pivot and a third flexible pivot, wherein movement of the second and third pivots by the linear actuators provides two degrees of rotational freedom to the reflective surface of the mirror with respect to the first flexible pivot. The linear actuators can be operatively associated with an optical disk drive controller so as to direct an optical beam to a selected disk location. In addition, the linear actuator and the optical disk drive controller can cooperate to manipulate the reflective surface so as to control tracking and focusing of the optical beam with respect to an optical disk.
The present invention is further directed to optical devices such as optical disk drives, which may be enhanced by incorporating one or more of the movable mirrors of the present invention to effectively switch a laser beam from at least one light source to one of a plurality outputs, such as read/write heads of an optical storage device.
The present invention is also directed to an apparatus and corresponding method for selectively directing a light beam from at least one light source to a number of outputs. The beam-directing apparatus uses at least one movable mirror having a reflective surface which is capable of changing its orientation to direct the light beam in a selected optical path. In a preferred embodiment, the beam-directing apparatus uses two movable mirrors, where each movable mirror is capable of rotating with respect to at least one pivot axis to selectively guide the light beam to one of the outputs.
According to one aspect of the invention, the beam-directing apparatus can be used with an optical disk drive for selectively coupling a beam of light from a laser module to a selected optical disk surface. In a preferred embodiment, the beam-directing apparatus uses two movable mirrors together with stationary mirrors. Each movable mirror is capable of rotating with respect to at least one pivot axis to guide the light beam to one of the stationery mirrors. According to the invention, the optical disk drive has a plurality of head members positioned near surfaces of a plurality of optical disks to optically read and/or write information from and onto the optical disks rotatably supported about a spindle. The head members preferably include at least one set of a head mirror and an R/W objective lens located between the head mirror and the respective disk for receiving the beam of light from the beam-directing apparatus and focusing the received light beam onto a selected track of the disk.
According to another aspect of the invention, one or more movable mirrors, of any suitable type, are used in the optical switching apparatus so as to enable the light beam to be rapidly and accurately guided along a precise optical path, as required by the optical disk drive. The movable mirrors may include a movable reflective surface which is adjustable about at least one pivot axis and preferably about two pivot axes. The movable mirror is associated with a control mechanism for precisely controlling the orientation of the reflective surface in one or both pivot axes. A processor may be coupled to the control mechanisms of the movable mirrors in order to coordinate their movements to selectively switch the optical path of the laser beam between different optical read/write head members.
According to a further aspect of the invention, a plurality of stationary mirrors is provided, each associated with one of said head members. The stationary mirrors have reflective surfaces oriented at a predetermined pivotal angle to deflect the light beam from the second movable mirror to a respective head member. Although referred to herein as xe2x80x9cstationaryxe2x80x9d, such mirrors may be mounted on and move with an actuator arm, but can be stationary with respect to the mount.
The reading and writing operations are executed by first moving the read/write head associated with such optical disk to a specific target track area thereof. The laser beam emitted by the laser source is reflected by the first and second movable mirrors to one of the stationary mirrors. A processor controls the movements of the first and second movable mirrors to precisely guide the light beam to a specific spot on the selected stationary mirror, such that the beam from the stationary mirror is deflected by a head mirror and guided to the center of an R/W objective lens associated with the selected optical disk. The beam reflected from the surface of the optical disk is monitored by a signal detector to reconstruct information stored on the recording surface of the disk.
In one aspect of the invention, the optical switching apparatus includes a feedback mechanism for monitoring the position of the movable mirrors. The feedback mechanism may include an auxiliary light source for generating an auxiliary light beam and a position sensitive detector for detecting the auxiliary light beam deflected from the movable mirror in order to accurately determine the position thereof.
In another aspect of the invention, an optical disk drive is provided in which a control mechanism is used with a beam-directing apparatus for controlling the operations of the beam-directing apparatus. The beam-directing apparatus may include two movable mirrors, the orientations of which are precisely controlled by the control mechanism. The movable mirrors together with the control mechanism are capable of rapidly and accurately guiding a light beam from a selected light source to a precise optical path.
In yet another aspect of the invention, an optical disk drive is provided in which the size of the beam reflected onto an optical disk surface may be controllable by a beam directing apparatus. The focusing of the beam on an optical disk surface may be controlled with use of two movable mirrors, accomplished by controlling the position of the laser beam impinging upon the second movable mirror with the first movable mirror. In a related aspect of the invention, the tracking of the beam on the optical disk surface may also be controlled by controlling the position of the laser beam impinging upon the second movable mirror with the first movable mirror.
In a further aspect of the invention, a movable mirror is provided. The movable mirror includes a reflector rotatable about at least one pivot axis. The reflector is adjustably supported between a support surface and at least one actuator so as to cause the reflector to rotate about pivot axis in either direction as the actuator moves toward or away the reflector. This movable mirror may be used in the read/write head members so that the orientation of its reflector may be adjusted, as required for focusing and tracking needs.


The invention provides X-ray contrastable plastics materials with low-molecular weight iodine compounds, a process for preparing X-ray contrastable plastics materials with low molecular weight iodine compounds, the use of low molecular weight iodine compounds to improve the X-ray contrast in transparent plastics materials and toys with improved X-ray contrast containing low molecular weight iodine compounds.

The invention provides X-ray contrastable plastics materials with low-molecular weight iodine compounds, a process for preparing X-ray contrastable moulding compositions with low molecular weight iodine compounds, the use of low molecular weight iodine compounds to improve the X-ray contrast in transparent plastics materials and toys with improved X-ray contrast containing low molecular weight iodine compounds.
Materials with the highest possible transparency and good mechanical characteristics which can be detected in the body by using X-rays are sought for the medical field and also for children""s toys. In contrast to metallic items, toys made of plastics are generally not detectable on an X-ray image. These types of moulding compositions can be made X-ray contrastable by means of suitable additives.
These types of moulding compositions were described, for example, in DE-A 195 45 289. In that patent, X-ray contrastable thermoplastic moulding compositions made of ABS with a BaSO4 additive were described.
X-ray detectable moulding compositions were also described in Silberman-Hazony, Encycl. Polym. Sci. Eng. (1988), 14, 1-8. Thermoplastic materials with various heavy metals as X-ray contrast agents were described. In addition, a halogen-containing terpolymer was mentioned.
Finally, FR 2223403 describes PVC and other vinyl polymers with iodine-containing salicylic acids, benzoic acids and their esters which resemble those in U.S. Pat. Nos. 3,361,700 and 3,645,955. However, PVC is not suitable for applications in which high transparency and good mechanical properties are required.
DE-A 197 26 191 and the patents U.S. Pat. No. 3,469,704 and DE-A 17 20 812 cited therein described transparent plastics moulding compositions made of polycarbonates with iodine-containing terminal groups. However, these can, under some circumstances, involve considerable additional synthesis costs because the polymer chains themselves have to be modified.
Finally, U.S. Pat. No. 3,382,207 discloses iodine-containing diphenyl carbonates as additives for polycarbonates.
Thus, the prior art does not currently provide any adequate X-ray contrastable plastics materials for use in transparent plastics parts. Due to its outstanding mechanical properties, polycarbonate has hitherto been used in particular for transparent toy parts which are subject to high mechanical stress. Now, it is intended to develop a type of plastics material that can be detected within the context of a conventional X-ray photograph while having unchanged high transparency and the smallest possible impairment to its mechanical properties. The thickness of layer in which the plastics material is still detectable should be as small as possible, but at most 1.2 mm.
The object was to develop moulding compositions using readily obtainable additives in standard thermoplastic materials which exhibit adequate contrast in X-ray images while also having good mechanical characteristics and transparency. The addition of heavy metals was to be avoided for toxicological reasons since materials for children""s toys were being sought.
Accordingly, the present application provides X-ray contrastable plastics materials containing at least one low molecular weight iodine compound, characterised in that the odine compound is present in amounts of 0.1 wt. % to 25 wt. % and is chosen from the lasses D-thyroxin, L-thyroxin, metrizamide, N,Nxe2x80x2-bis-(2,3-dihydroxypropyl)-5-[N-(2,3-dihydroxypropyl)-acetamido]-3,4,6-triiodoisophthalamide, xcex1-(2,4,6-triiodophenoxy)-butyric acid, beta-bromo-2,4,6-triiodophenetols, ethylene glycol-4-(iodophenyl)-methylether-methylether and aromatic compounds in accordance with the following general formulae (I), (II), (III)
wherein R, Rxe2x80x2, Rxe2x80x3, Rxe2x80x2xe2x80x3=COOH, OH, NHCORxe2x80x3xe2x80x3, CONHRxe2x80x3xe2x80x3, ORxe2x80x3xe2x80x3, Cl, Br, F, Rxe2x80x3xe2x80x3, where Rxe2x80x3xe2x80x3 may be H or a linear or branched alkyl group with 1-18 carbon atoms. Furthermore, l=0 to 5, m=0 to 5xe2x88x92l, n=0 to 3, o=0 to 3xe2x88x92n p=0 to 4, q=0 to 4xe2x88x92p, r=0 to 4, s=0 to 4xe2x88x92r, t=0 to 5, u=0 to 5xe2x88x92t.
To prepare metrizamide see J. Cell. Biol. 1991, 113, 45, to prepare Iohexol(copyright) (N,Nxe2x80x2-bis-(2,3-dihydroxypropyl)-5-[N-(2,3-dihydroxypropyl)-acetamido]-3,4,6-triiodoisophthalamide) see Sigma-Aldrich Chemie GmbH, Steinheim, Germany, to prepare Baygnostil(copyright) (xcex1-(2,4,6-triodophenoxy)butyric acid) see Bayer AG, Leverkusen, Germany.
Mixtures of all the iodine-containing compounds mentioned above are also suitable.
The following are particularly suitable: 4,4xe2x80x2-diiodobiphenyl, 2,3,5-triiodobenzoic acid, 2,4,6-triiodophenol, 4-iodophenol, 3-iodophenol, 2-iodophenol, 3,5-diiodosalicylic acid, 3,5-diiodo-2-hydroxybenzoic acid, 4-iodobenzoic acid, 3-iodobenzoic acid, 2-iodobenzoic acid, 2,6-dimethyl-4-iodophenol, 2-iodo-4-phenylphenol, 3,3xe2x80x2-diiodo-2,2xe2x80x2,6,6xe2x80x2-tetramethyl-4,4xe2x80x2-biphenol, 2,6-diiodo-4-methylphenol, 3,5-diiodo-2-hydroxybenzoic acid, 2,4-dichloro-6-iodophenol, 1,4-dimethoxy-2,3-dimethyl-5-iodobenzene, 1,2-dimethoxy-4-iodobenzene, 2,2xe2x80x2-diiodo-4,4xe2x80x2,5,5xe2x80x2-tetramethoxybiphenyl, 4-iodo-3-phenylanisol, 1,2-dimethoxy-3,4-dimethyl-5-iodobenzene, 2,2xe2x80x2-diodo-3,3xe2x80x2-dimethyl-4,4xe2x80x2,5,5xe2x80x2-tetramethoxybiphenyl, 1,4-dimethoxy-2-iodo-5-methylbenzene, 1,2-dimethoxy-4-iodo-5-methylbenzene, 1,2-diiodo-4,5-dimethoxybenzene, 2,2xe2x80x2-diiodo-3,3xe2x80x2,4,4xe2x80x2,5,5xe2x80x2-hexamethoxybiphenyl, 2,2xe2x80x2-diiodo-4,4xe2x80x2-dimethoxy-3,3xe2x80x2,5,5xe2x80x2-tetramethylbiphenyl, very particularly 4,4xe2x80x2-diiodobiphenyl.
The X-ray contrastable plastics materials contain the low molecular weight iodine compound in amounts between 0.5 and 20 wt. %, preferably between 0.8 and 10 wt. % and particularly preferably between 1 and 5 wt. %.
Transparent thermoplastic materials are preferably used as transparent plastics, particularly preferably the polymers of ethylenically unsaturated monomers and/or polycondensates of bifunctional reactive compounds.
Particularly suitable plastics are polycarbonates or copolycarbonates based on diphenols, polyacrylates or copolyacrylates and polymethacrylates or copolymethacrylates such as e.g. polymethylmethacrylate or copolymethylmethacrylate, or else copolymers with styrene such as e.g. transparent polystyrene/acrylonitrile (SAN), also transparent cycloolefins, polycondensates or copolycondensates of terephthalic acid, such as e.g. polyethylene terephthalate or copolyethylene terephthalate (PET or COPET) or glycol-modified PET.
A person skilled in the art produces exceptional results with polycarbonates or copolycarbonates.
Thermoplastic, aromatic polycarbonates in the context of the present invention are either homopolycarbonates or copolycarbonates; the polycarbonates may be linear or branched in a known manner.
These polycarbonates are prepared in a known manner from diphenols, carbonic acid derivatives, optional chain stoppers and optional branching agents.
Details of the preparation of polycarbonates have been presented in many patent documents over the last 40 years. By way of example, reference is made here only to Schnell, xe2x80x9cChemistry and Physics of Polycarbonatesxe2x80x9d, Polymer Reviews, volume 9, Interscience Publishers, New York, London, Sydney, 1964, to D. Freitag, U. Grigo, P. R. Mxc3xcller, H. Nouvertnxc3xa9, BAYER AG, xe2x80x9cPolycarbonatesxe2x80x9d in Encyclopedia of Polymer Science and Engineering, volume 11, 2nd edition, 1988, pages 648-718 and finally to Drs. U. Grigo, K. Kirchner and P. R. Mxc3xcller xe2x80x9cPolycarbonatexe2x80x9d in Becker/Braun, Kunststoff-Handbuch, vol. 3/1, Polycarbonate, Polyacetale, Polyester, Celluloseester, Carl Hanser Verlag, Munich, Vienna 1992, pages 117-299.
Suitable diphenols for preparing polycarbonates are, for example, hydroquinone, resorcinol, dihydroxydiphenyls, bis-(hydroxyphenyl)-alkanes, bis-(hydroxyphenyl)-cycloalkanes, bis-(hydroxyphenyl)-sulfides, bis-(hydroxyphenyl)-ethers, bis-(hydroxyphenyl)-ketones, bis-(hydroxyphenyl)-sulfones, bis-(hydroxyphenyl)-sulfoxides, xcex1,xcex1xe2x80x2-bis-(hydroxyphenyl)-diisopropylbenzenes, and their ring-alkylated and ring-halogenated compounds.
Preferred diphenols are 4,4xe2x80x2-dihydroxydiphenyl, 2,2-bis-(4-hydroxyphenyl)-propane, 2,4-bis-(4-hydroxyphenyl)-2-methylbutane, 1,1-bis-(4-hydroxyphenyl)-p-diisopropyl-benzene, 2,2-bis-(3-methyl-4-hydroxyphenyl)-propane, 2,2-bis-(3-chloro-4-hydroxyphenyl)-propane, bis-(3,5-dimethyl-4-hydroxyphenyl)-methane, 2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane, bis-(3,5-dimethyl-4-hydroxyphenyl)-sulfone, 2,4-bis-(3,5-dimethyl-4-hydroxyphenyl)-2-methylbutane, 1,1-bis-(3,5-dimethyl-4-hydroxyphenyl)-p-diisopropylbenzene, 2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane, 2,2-bis-(3,5-dibromo-4-hydroxyphenyl)-propane and 1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane.
Particularly preferred diphenols are 2,2-bis-(4-hydroxyphenyl)-propane, 2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane, 2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane, 2,2-bis-(3,5-dibromo-4-hydroxyphenyl)-propane, 1,1-bis-(4-hydroxyphenyl)-cyclohexane and 1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane.
These and other suitable diphenols are described, for example, in U.S. Pat. Nos. 3,028,635, 2,999,835, 3,148,172, 2,991,273, 3,271,367, 4,982,014 and 2,999,846, in German patent documents 1 570 703, 2 063 050, 2 036 052, 2 211 956 and 3 832 396, in French patent document 1 561 518, in the monograph xe2x80x9cH. Schnell, Chemistry and Physics of Polycarbonates, Interscience Publishers, New York 1964xe2x80x9d and in Japanese patent documents 62039/1986, 62040/1986 and 105550/1986.
In the case of homopolycarbonates, only one diphenol is used; in the case of copolycarbonates, several diphenols are used.
Suitable carbonic acid derivatives are, for example, phosgene or diphenyl carbonate.
Suitable chain stoppers are either monophenols or monocarboxylic acids. Suitable monophenols are phenol itself, alkylphenols such as cresols, p-tert.-butylphenol, p-n-octylphenol, p-iso-octylphenol, p-n-nonylphenol and p-iso-nonylphenol, halogenophenols such as p-chlorophenol, 2,4-dichlorophenol, p-bromophenol and 2,4,6-tribromophenol and mixtures of these.
The preferred chain stopper is p-tert.-butylphenol.
Suitable monocarboxylic acids are benzoic acid, alkylbenzoic acids and halogenobenzoic acids.
Preferred chain stoppers are phenols of the formula (I)
in which R is hydrogen, tert.-butyl or a branched or unbranched C8 and/or C9 alkyl group.
The amount of chain stopper to be used is 0.1 mol. % to 5 mol. %, with respect to the particular diphenols used. The addition of chain stoppers may take place before, during or after phosgenation.
Suitable branching agents are the trifunctional or more than trifunctional compounds known from polycarbonate chemistry, in particular those with three or more than three phenolic OH groups.
Suitable branching agents are, for example, phloroglucine, 4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)-hept-2-ene, 4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)-heptane, 1,3,5-tri-(4-hydroxyphenyl)-benzene, 1,1,1-tri-(4-hydroxyphenyl)-ethane, tri-(4-hydroxyphenyl)-phenylmethane, 2,2-bis-[4,4-bis-(4-hydroxyphenyl)-cyclohexyl]-propane, 2,4-bis-(4-hydroxyphenyl-isopropyl)-phenol, 2,6-bis-(2-hydroxy-5xe2x80x2-methylbenzyl)-4-methyl-phenol, 2-(4-hydroxyphenyl)-2-(2,4-dihydroxyphenyl)-propane, hexa-(4-(4-hydroxyphenyl-isopropyl)-phenyl orthoterephthalate, tetra-(4-hydroxyphenyl)-methane, tetra-(4-(4-hydroxyphenyl-isopropyl)-phenoxy)-methane and 1,4-bis-(4xe2x80x2,4xe2x80x3-dihydroxytriphenyl)-methyl)-benzene and also 2,4-dihydroxybenzoic acid, trimesic acid, cyanuric chloride and 3,3-bis-(3-methyl-4-hydroxyphenyl)-2-oxo-2,3-hydroindole.
The amount of optionally used branching agent is 0.05 mol. % to 2 mol. %, again with respect to the particular diphenols used.
The branching agent may either be initially introduced in the aqueous alkaline phase with the diphenols and the chain stoppers or may be added before phosgenation, dissolved in an organic solvent. In the case of a transesterification process, the branching agent is used together with the diphenols.
All these steps for preparing thermoplastic polycarbonates are familiar to a person skilled in the art.
Naturally, the plastics material makes up the major proportion of the compositions so that it is generally present in amounts between 75.0 and 99.9 wt. %, preferably 80 and 99.8 wt. %, particularly preferably between 90 and 99.2 wt. % and very particularly preferably between 95 and 99 wt. %, with respect to the entire mixture.
In order to achieve improved formulations, it is possible that in addition at least further additive which is conventionally present in thermoplastic plastics, preferably polycarbonates and copolycarbonates is also present, such as e.g. stabilisers (such as described e.g. in EP 0 839 623 A1 or EP 0 500 496 A1), especially heat stabilisers, in particular organic phosphites or phosphines, mould release agents, for example fatty acid esters of glycerine or tetramethanolmethane, wherein unsaturated fatty acid may also be fully or partly epoxidised, in particular glycerine monostearate or pentaerythrityl tetrastearate (PETS), flame retardants, antistatic agents, UV absorbers, for example triazoles, fillers, foaming agents, colorants, pigments, optical brighteners, transesterification catalysts and nucleating agents etc., preferably in amounts of up to 5 wt. % each, preferably 0.01 to 5 wt. %, with respect to the entire mixture, particularly preferably 0.01 to 1 wt. % with respect to the amount of plastics material as described, for example, in EP 0 839 623 A1 or EP 0 500 496 A1.
Mixtures of these additives are also possible.
The X-ray opaque polymer compositions obtained in this way may be converted into shaped items such as, for example, toy parts, but also fibres, films, strips, sheets, multi-wall sheets, vessels, pipes and other sections, using conventional methods such as, for example, hot compression, spinning, extrusion or injection moulding. The polymer compositions may also be processed to give cast films. The invention therefore also provides use of the polymer compositions according to the invention to produce a shaped item. The use of multi-layered systems is also of interest. In this case, a polymer composition according to the invention with a relatively high concentration of bromine or iodine-containing additives is applied in a thin layer to a shaped item made from a polymer which is X-ray transparent. Application may take place at the same time as or immediately after shaping the underlying item, e.g. by coextrusion or multi-component injection moulding. Application may also take place, however, to the final shaped underlying item, e.g. by lamination with a film or by coating with a solution. The moulding compositions are especially suitable for transparent children""s toy parts or for medical applications. Such moulded parts are especially suitable for small parts of children""s toys.

Plastic molding materials which can be detected by X-ray contrast


Embodiments of the present disclosure relate to methods and systems for on-demand next-hop resolution. Aspects of the embodiments include receiving a triggering event to prompt a request for a path to a network location; requesting a path computation from a second network element based on receiving the triggering event; receiving the path computation from the second network element; and programming an output interface with an indication of the path computation received from the second network element.

On-Demand Routing (ODR) is an enhancement to Cisco Discovery Protocol (CDP), a protocol used to discover other Cisco devices on either broadcast or non-broadcast media. With the help of CDP, it is possible to find the device type, the Internet Protocol (IP) address, the Cisco IOS® version running on the neighbor Cisco device, the capabilities of the neighbor device, and so on. In Cisco IOS software release 11.2, ODR was added to CDP to advertise the connected IP prefix of a stub router via CDP. This feature takes an extra five bytes for each network or subnet, four bytes for the IP address, and one byte to advertise the subnet mask along with the IP. ODR is able to carry Variable Length Subnet Mask (VLSM) information.